1. Field of the Invention
This invention relates generally to rotary engines and more particularly to rotary opposed-piston engines.
2. Description of the Related Art
The vast majority of internal combustion engines currently in use are reciprocating engines in which a piston moves up and down within a cylinder. The linear motion of the piston is translated into rotary motion by a crankshaft connected to the piston by a piston rod. In a typical engine, due to the large forces involved, the coupling between the crankshaft and the piston rod and between the piston and the piston rod, is a simple journal bearing. Accordingly, significant friction is introduced when converting the reciprocating motion of the piston to rotary motion. Furthermore, the power output on the crankshaft is not constant. As the piston drives the crankshaft, the crankshaft rotates and changes the effective length of the lever arm between the piston and the crankshaft.
Current internal combustion engines further require complicated valving mechanisms in order to introduce fuel and air into the cylinder and to release exhaust gases. Typically such mechanisms involve spring loaded valves that are biased toward the closed position. Cams, driven by the crankshaft open and close the valves at appropriate times by pushing against valve stems attached to the valves. The contact between the cam and the valve stems is typically a sliding contact introducing a great deal of friction just to open the valve.
Rotary engines eliminate many of these problems. In one type of rotary engine, the pistons move within a donut shaped chamber, or toroid, and are attached to an output shaft at the center of the toroid. The piston moves along an arcuate path, defined by the toroidal chamber, directly causing the output shaft to rotate. Accordingly, no translation from reciprocating to rotary motion is required.
The complicated valving systems of the reciprocating engine may be replaced in a rotary engine by simple apertures in the toroidal chamber. As the pistons move along the toroidal chamber, they move past the apertures drawing in air and expelling exhaust. A sealed combustion chamber is achieved by simply combusting the fuel air mixture in a portion of the toroidal chamber in which no apertures are formed.
What is currently lacking in the art is a practical rotary engine. Prior attempts have not been commercially viable and do not overcome critical challenges. The primary obstacle to achieving a practical rotary engine lies in the shape of the chamber itself. In a reciprocating engine a combustion chamber is defined by the top surface of the cylinder, the wall of the cylinder, and the piston. The combustion chamber traps expanding gases, forcing the piston to move. In a rotary engine, one must find a way to define a combustion chamber within a toroidal chamber with no top surface, as in a cylinder.
Two possible solutions to this problem exist. First, one may place a fixed barrier within the toroidal chamber. Accordingly, the piston, the barrier, and the walls of the toroid define a combustion chamber. Second, one may use two opposed pistons, fixing a first piston and allowing a second piston to move, then fixing the second piston and allowing the first piston to move. Thus a combustion chamber is defined by the two pistons and the walls of the toroid.
Defining a fixed barrier is problematic because the piston must constantly change direction once it reaches the barrier. Opposed pistons do not have this problem, in as much as both pistons can be allowed to move within the toroid. However, both types of rotary engine must have some mechanism to control the movement of the piston, whether to reverse direction when needed or to fix the position of the piston in order to define a combustion chamber. Both types must also translate the discontinuous velocity of a piston into a substantially constant rotation of an output shaft. Prior systems provide no adequate means to control the pistons providing a smooth output at high output torques.
Some designs, for example, use mechanisms to obstruct the movement of the piston in order to fix its position. In one system, stop pins are moved into place to stop the piston. However, such systems simply obstruct the motion of the piston. Accordingly, at high angular velocities the piston will repeatedly strike the stopping mechanism at high speeds causing premature breakage. Prior designs also provide no blending of motion to give a smooth output torque. Motion of the piston in prior systems is simply rectified to the correct rotational direction but is not controlled to provide a smooth angular velocity output. In addition to providing a low quality output, such systems are subject to a great deal of mechanical shock, clatter, wear, and breakage, regardless of load, resulting in a very short useful life.
Accordingly, it would be an advancement in the art to provide a rotary opposed-piston engine providing a substantially constant output. Such a system should control the motion of the pistons to define a combustion chamber while reducing mechanical shock to the components thereof.